1. Field of the Invention
The present invention relates to a display apparatus that uses electrophoretic elements.
2. Description of the Related Art
It is noted that various forms of paper-type display apparatuses are recently being developed. Such display apparatus technology may be applied to an electronic book that is configured to display an image of one page (frame) of a document on a display unit at one time and successively switch the pages (frames) being displayed to enable a user to virtually turn the pages of the document at a desired speed in a manner similar to turning the pages of an actual book, for example. A display apparatus that uses electrophoretic elements is known as one form of such paper-type display apparatus. FIGS. 1-3 are diagrams illustrating a configuration of a display apparatus that uses electrophoretic elements according one prior art example.
FIG. 1 is a first diagram illustrating a configuration of a display apparatus 100 according to the prior art. FIG. 2 is a second diagram illustrating a configuration of the display apparatus 100. FIG. 3 is an enlarged view of a thin film transistor (TFT) 105 of the display apparatus 100.
As is shown in FIG. 1, the display apparatus 100 includes a display unit 120 and a drive circuit 130 that drives the display unit 120.
In the following, the display unit 120 is described with reference to FIGS. 1 and 2.
The display unit 120 includes an electrode substrate 101A and a circuit substrate 102A that oppose each other (see FIG. 2). The electrode substrate 101A includes a transparent common electrode 101; and the circuit substrate 102A includes thin film transistors (TFT) 105, scanning lines 106, and signal lines 107. The circuit substrate 102A also includes pixel electrodes 102 that are arranged into a matrix pattern on top of the thin film transistors (TFT) 105, the scanning lines 106, and the signal lines 107.
As is shown in FIG. 2, a liquid having positively or negatively charged white electrophoretic particles (elements) 103 and black electrophoretic particles (elements) 104 scattered within is sealed between the common electrode 101 and the pixel electrode 102. It is noted that the white electrophoretic elements 103 and the black electrophoretic elements 104 are charged by differing electrical charges. Also, a fixed voltage is applied to the common electrode 101 arranged on the electrode substrate 101A. The pixel electrodes 102 arranged on the circuit substrate 102A are each conductively connected to source electrodes of the TFT 105 arranged on the circuit substrate 102A (see FIG. 3).
With respect to the TFTs 105 arranged on the circuit substrate 102A, when the TFTs 105 are arranged in the line directions, their gate electrodes 112 are connected to the scanning lines 106 (see FIG. 3). On the other hand, when the TFTs 105 are arranged in the row directions, their gate electrodes 112 are connected to the signal lines 107 of the circuit substrate 102A (not shown).
The TFT 105 controls the amount of current flowing between a source electrode 113 and a drain electrode 114 with the voltage applied to its gate electrode 112. It is noted that when the source-drain current of the TFT 105 is large, a switch of the TFT 105 is turned on, and when the source-drain current of the TFT 105 is small, the switch of the TFT 105 is turned off.
The drive circuit 130 includes a controller 108, a memory 109, a scanning line driver 110, and a signal line driver 111. The controller 108 controls display operations of the display apparatus 100. The memory 109 stores display data for each pixel forming a pattern of plural frames to be displayed on the display apparatus 100.
In the following, operations of the display apparatus 100 are described with reference to FIG. 1.
In the case of displaying a new frame on the display apparatus 100, a scanning command signal 10B is transmitted from the controller 108 to the scanning driver 110. In response to receiving the scanning command signal 10B, the scanning line driver 110 applies corresponding voltages to the gate electrodes 112 of the TFTs 105 via the scanning lines 106 to control the switching operations of the TFTs 105. It is noted that the scanning command signal 10B from the controller 108 includes a control signal for determining the TFTs that are to be turned on, and a control signal for determining the output timing of the voltages to be output from the scanning line driver 110.
Also, the controller 108 transmits an addressing signal 10A to the memory 109 and a display command signal 10C to the signal line driver 111. At the memory 109, display data 10D of each pixel forming a pattern of the frame to be displayed are extracted based on the addressing signal 10A. Then, the extracted display data 10D are transmitted to the signal line driver 111.
The signal line driver 111 applies corresponding voltages to the gate electrodes 112 of the TFTs 105 via the signal line 107 based on the display command signal 10C and the display data 10D. It is noted that the display command signal 10C from the controller 108 includes a control signal for determining the timing at which the voltage is to be output from the signal line driver 111.
When the TFT is turned on, the voltage applied to the gate electrode 120 of the TFT 105 is applied to the pixel electrode 102. The pixel electrode 102 is applied a positive voltage or a negative voltage. In turn, an electric field is generated by the difference in potential between the pixel electrode 102 and the common electrode 101 so that the white electrophoretic elements 103 or the black electrophoretic elements 104 move to the common electrode 101 side. In this way, a pattern may be displayed on the common electrode 101 side.
As can be appreciated, displaying a frame on the display apparatus 100 involves successively turning on TFTs 105 that are connected to the scanning lines 106 based on the scanning command signal 10B, and the frame display operations may be completed at the time desired patterns are displayed by all the pixel electrodes 102 connected to the TFTs 105. In the following descriptions, the process of successively turning on the TFTs 105 is referred to as scanning.
In the following, frame switching operations performed at the display apparatus 100 are described with reference to FIGS. 4 and 5. FIG. 4 is a diagram illustrating an exemplary display unit of the display apparatus 100. FIG. 5 is a timing chart illustrating frame switching operations of the display apparatus 100.
The illustrated display unit A01 of FIG. 4 has scanning lines X1-X6 and signal lines Y1-Y8. It is noted that scanning lines X1-Xm of the timing chart of FIG. 5 corresponds to the scanning lines X1-X6 of the display unit A01, and the signal lines Y1-Yn of the timing chart of FIG. 5 corresponds to the signal lines Y1-Y8 of the display unit A01. Also, it is assumed in the following descriptions that the display status of the display unit A01 at an initial stage corresponds to the display status A of FIG. 5, and the display status of the display unit A01 is switched from display status A to display status B and then from display status B to display apparatus C of FIG. 5.
In the display apparatus 100, the scanning lines X1-X6 of the display unit A01 are successively scanned from scanning line X1 to scanning line X6. Specifically, switching control operations are performed for successively turning on the TFTs 105 connected to the scanning lines X1 through X6. It is noted that in the present case, when the source-drain current of the TFT 105 is at high level (H level), the TFT 105 is turned off, and when the source-drain current of the TFT 105 is at low level L level), the TFT 105 is turned on.
In the display unit A01, after the elapse of scanning time B02 corresponding to the time required for completing one scanning process, voltages for displaying patterns representing the display status B of FIG. 5 are applied to the pixel electrodes 102.
Then, the white electrophoretic elements 103 and the black electrophoretic elements 104 are moved as a result of the generation of an electric field between the pixel electrodes 102 and the common electrode 101, and the pixel electrodes 102 are switched from one color pattern to another color pattern. After the elapse of pixel pattern switching time B01 corresponding to the time required for the pixel electrodes 102 to be switched to a different color pattern, the display status of the display unit A01 is switched from the display status A to the display status B of FIG. 5.
As can be appreciated from the above descriptions, in switching the frame displayed on the display unit A01 of the display apparatus 100, the display switching time required for switching a display of one frame is equal to the total of the scanning time and the pixel pattern switching time.
The scanning time of the display apparatus 100 corresponds to the process time required for scanning the scanning lines 106 and applying voltages to the pixel electrodes 102. It is noted that only a very short time is required for applying voltages to the pixel electrodes 102 so that the scanning time is substantially shorter than the pixel pattern switching time. Therefore, the required time for displaying one frame relies largely on the pixel pattern switching time.
The pixel pattern switching time of the display apparatus 100 is around several dozen to several hundred milliseconds (ms) which time is substantially longer than the display switching time for other types of display apparatuses such as the liquid crystal display. It is noted that the pixel pattern switching time depends on characteristics of the electrophoretic elements and is fixed regardless of the display method used. Accordingly, it is difficult to reduce the display switching time for switching the displayed frame by reducing the pixel pattern switching time.
Also, the display apparatus may successively switch and display plural frames in order to display a desired frame. For example, with respect to an electronic document including plural pages (frames), a user may turn the pages of the electronic document one page at a time and check the contents of each page to search a desired page. In such a case, since a relatively long display switching time is required in the conventional display apparatus using electronphoretic elements, a relatively long period of time may be required before the desired page may be displayed.
Also, it is noted that in the conventional display apparatus that uses electrophoretic elements, the speed at which the pages are turned cannot be adjusted. Therefore, it may take a long period of time before a desired page is displayed when a large number of pages have to be turned to reach the desired page, for example.